Read receipts are a way for people to acknowledge that they have received your email. The recipient can normally choose whether to acknowledge the receipt or not, so they are not a completely reliable way of checking if your emails have been received by someone.

You can request read receipts by selecting OptionsRequest Read Receipt in the menu of the composer window or clicking the corresponding toolbar icon.

For read receipts that you receive you can define Evolution's behavior under Message Receipts in the Composing Messages section of the account preferences.